This invention relates to piping systems for pulp dryers and methods for piping heat exchangers thereof.
Pulp dryers commonly use a plurality of blow boxes to dry moving, continuous webs of wood pulp with hot air. The hot air is circulated by means of a plurality of fans. The air is heated, typically by steam heat exchangers or "steam coils" assembled in vertical banks, before the air is directed onto the web of pulp.
In one common arrangement, a plurality of fans arc vertically-spaced apart. There is a pair of spaced-apart heat exchanger banks on each side of each fan. Each bank has several heat exchangers. There is an access door between each such pair of heat exchangers. The air moves towards the access door between the heat exchangers. The air then splits into two streams and moves through the heat exchangers which are positioned to each side of the door. Each such steam changes direction again and passes through one of the fans which blows the air towards the blow boxes and onto the web.
Conventionally the heat exchangers are connected to two vertical conduits in each bank which extend between each vertically-spaced apart set of heat exchangers. There is a first connecting conduit connecting each heat exchanger to a steam feed conduit which feeds steam to each heat exchanger. There is a second connecting conduit connecting each heat exchanger to a condensate conduit which carries away condensate and steam from each heat exchanger.
Conventionally the steam feed conduit and the condensate conduit are positioned adjacent the sides of the heat exchanger which receive the stream of air or discharge the heated air. Likewise the connecting conduits usually extend over these sides of each heat exchanger as well. Thus the conduits partially block the stream of air and reduce the efficiency of each heat exchanger.
Furthermore, the positions of the conduits interfere with servicing of the heat exchangers. For example, each heat exchanger typically has a screen accessible through the access door. The conduits extend over the screens, making cleaning, removal and replacement of the screens more difficult. Similarly, the conduits interfere with removal and replacement of the heat exchangers themselves.
Referring to FIG. 1, this shows a portion of a conventional pulp dryer according to the prior art. Each such pulp dryer has a plurality of fans 10, each powered by a motor 12. The air is heated by a steam heat exchanger or steam coil 14 which is equipped with a screen 16. There is a similar heat exchanger on the opposite side of the fan (not shown). The steam coils are arranged in spaced-apart pairs, another such heat exchanger being positioned to the right of the one shown in FIG. 1. Air passes between the heat exchangers as indicated by arrow 18. The air then splits into two portions, one portion moving through heat exchanger 14 as indicated by arrows 20 and 22. The air is directed by the fan toward the blow boxes which provide air to the pulp web as indicated by arrow 23.
The conventional piping arrangement shown in FIG. 1 includes a plurality of condensate conduits 24 which extend vertically. These receive condensate from heat exchanger 14 and a plurality of heat exchangers similar to heat exchanger 14 positioned above and below heat exchanger 14. Similarly, a steam feed conduit 26 extends vertically and is used to provide steam to each of the vertically spaced-apart heat exchangers including heat exchanger 14.
There is a first connecting conduit 30 which connects the steam feed conduit 26 to the heat exchanger. Conduit 30 includes an elongated pipe 32 and connecting flanges 34. Likewise there is second connecting conduit 36 which connects heat exchanger 14 to condensate conduit 24. This includes an elongated conduit 38 and flanges 40. These conduits 28 and 30 connect to opposite ends of the heat exchanger. In other prior art heat exchangers one or both conduits connect midway between the ends.
There is an access doorway 42 in front of the heat exchanger 14 which is normally closed by a door. This provides access to heat exchanger 14 as well as a similar heat exchanger located to the right of heat exchanger 14, but not shown. It may be seen that the position of the condensate conduit 24 and second connecting conduit 36, particularly elongated conduit 38 thereof, interfere with access to screen 16 and heat exchanger 14. This makes it difficult to remove or replace the screen or the heat exchanger. Also the condensate conduit 24, connecting conduit 36, steam feed conduit 26 and connecting conduit 32 all interfere with air flow through the heat exchanger. Workers entering the doorway are exposed to hot steam pipes with this configuration.
Accordingly, there is a need for a more efficient piping system for pulp dryers which does not interfere with air flow through the heat exchangers and allows easy access to the heat exchangers and screens thereof by personnel entering through the access doors.